# What is THCA?

> THCA (tetrahydrocannabinolic acid) is the acid form of THC that the living cannabis plant actually makes and stores in its trichome heads. Fresh and dried flower is mostly THCA, not THC. Heat (smoking, vaping, baking) removes a CO2 molecule and turns THCA into THC. Labels report total THC = THC + 0.877 × THCA, so 30% THCA means about 26% total THC.

- Canonical: https://genetixbay.com/knowledge/answers/what-is-thca.html
- Topic: Basics · Type: Definition
- Evidence: Established · Status: Draft: awaiting expert review
- Full article: [Buyer beware: potency labels, strain names and other claims that don't hold up](https://genetixbay.com/knowledge/basics/buyer-beware-label-claims.md)
- Also asked as: THCA vs THC | Is THCA the same as THC? | Does raw weed have THC? | What does total THC mean on a label?
- Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)"

## Short answer

[THCA](https://genetixbay.com/knowledge/glossary/thca.md) (tetrahydrocannabinolic acid) is the form of [THC](https://genetixbay.com/knowledge/glossary/thc.md) the cannabis plant actually makes. Fresh and dried buds are mostly THCA; heat turns it into THC. Labels give total THC = THC + [0.877](https://genetixbay.com/knowledge/glossary/total-thc.md) × THCA, so 30% THCA is about 26% total THC. *Established* chemistry.

## Why

The plant makes acids. Secretory cells in the glandular [trichomes](https://genetixbay.com/knowledge/glossary/trichome.md) make [cannabinoid](https://genetixbay.com/knowledge/glossary/cannabinoid.md) acids, THCA among them, and store them in the gland head [2]. They become neutral THC mainly by heat, not on the living plant [3].

Heat knocks off a [carbon dioxide](https://genetixbay.com/knowledge/glossary/co2-enrichment.md). That reaction, [decarboxylation](https://genetixbay.com/knowledge/glossary/decarboxylation.md), was measured at 80–145 °C: THCA converted to THC following first-order kinetics, faster at higher temperatures, and faster than [CBDA](https://genetixbay.com/knowledge/glossary/cbda.md) or [CBGA](https://genetixbay.com/knowledge/glossary/cbga.md) [1]. Smoking, vaping and baking all do it.

The 0.877 factor is just molecular weight. THC weighs about 314.5 g/mol and THCA about 358.5 g/mol, so 1 g of THCA can become at most 0.877 g of THC. Real conversion is usually less than complete.

Labels can run high. A retest of retail flower found many products below their labelled THC [4]. GenetixBay's position: flower labelled above about 35% [total cannabinoids](https://genetixbay.com/knowledge/glossary/total-cannabinoids.md) isn't credible.

## The numbers

| Measure | Meaning | Example |
|---|---|---|
| THCA % | Acid form in the bud | 25% |
| THC % (delta-9) | Already neutral; usually small in fresh flower | 1% |
| Total THC | THC + 0.877 × THCA | 1 + 21.9 ≈ 22.9% |
| 0.877 | 314.5 ÷ 358.5 g/mol | — |
| Ceiling for flower | Total cannabinoids above ~35% not credible | — |

## What to do

1. Read a [certificate of analysis](https://genetixbay.com/knowledge/glossary/coa.md) for both THCA and THC, and the total.
2. Treat "THCA flower" as ordinary cannabis: heat converts it.
3. Store buds cool, dark and airtight to slow conversion and oxidation.
4. Check local rules: some places regulate by total THC, others by delta-9 only.

## Common mistakes

- Thinking high-THCA flower is "not THC".
- Adding THCA and THC without the 0.877 factor.
- Trusting a 40%+ flower label.

## Related

- Full article: [Buyer beware: label claims](https://genetixbay.com/knowledge/basics/buyer-beware-label-claims.md)
- Answers: [THC vs CBD plants](https://genetixbay.com/knowledge/answers/thc-vs-cbd-plants.md) · [checking trichomes](https://genetixbay.com/knowledge/answers/how-to-check-trichomes.md)
- Article: [Cannabis plant biology](https://genetixbay.com/knowledge/basics/cannabis-plant-biology.md)
- Terms: [THCA](https://genetixbay.com/knowledge/glossary/thca.md) · [decarboxylation](https://genetixbay.com/knowledge/glossary/decarboxylation.md) · [total THC](https://genetixbay.com/knowledge/glossary/total-thc.md)

## Follow-up questions

**How is total THC calculated?** Total THC on a cannabis label is calculated as THC + 0.877 × THCA. The 0.877 factor is the mass ratio of THC to THCA, about 314.5 / 358.5 g/mol: heating removes a carbon dioxide molecule from each THCA molecule, so 1 g of THCA becomes at most 0.877 g of THC. A bud with 30% THCA therefore has about 26% total THC.

**Does raw cannabis contain THC?** Raw cannabis contains mostly THCA and only a little neutral THC. The plant makes cannabinoids as acids in its glandular trichomes, and they convert to neutral THC mainly when heated, not on the living plant. Some THCA converts slowly during drying, curing and storage, and much faster above about 100 °C. Effects are reported, not promised.

**Can flower really test 35% THCA?** Flower labelled above about 35% total cannabinoids is not credible, in GenetixBay's position. Cannabinoids are made only in trichome heads, and most of a bud's dry weight is bract, stem and leaf. A 42% total THC label would need about 48% THCA in the dry bud, which only a lump of resin, not flower, could reach.

## Sources

1. Wang M, Wang YH, Avula B, et al. 2016. Decarboxylation study of acidic cannabinoids: a novel approach using ultra-high-performance supercritical fluid chromatography/photodiode array-mass spectrometry. Cannabis and Cannabinoid Research 1(1):262-271. https://doi.org/10.1089/can.2016.0020
2. Livingston SJ, Quilichini TD, Booth JK, et al. 2020. Cannabis glandular trichomes alter morphology and metabolite content during flower maturation. The Plant Journal 101(1):37-56. https://doi.org/10.1111/tpj.14516
3. Small E. 2015. Evolution and classification of Cannabis sativa (marijuana, hemp) in relation to human utilization. Botanical Review 81:189-294. https://doi.org/10.1007/s12229-015-9157-3
4. Schwabe AL, Johnson V, Harrelson J, McGlaughlin ME. 2023. Uncomfortably high: Testing reveals inflated THC potency on retail Cannabis labels. PLOS ONE 18(4):e0282396. https://doi.org/10.1371/journal.pone.0282396